Dynamoelectric machines come in widely varying shapes, sizes and capacities. Some dynamoelectric machines are employed as motors while others are employed as generators. Some are employed as motor-generators, meaning they can be operated either as a motor or as a generator depending upon exactly what function is desired of the machine at a given point in time.
In some cases, volume and weight constraints are minimal while in others they are critical. For example, in aerodynamic applications, weight is always a concern and volume constraints are necessary lest the machine occupy too much volume of a vehicle or even contribute to a less efficient aerodynamic shape as a result of the bulk of the machine. Further, in aerodynamic applications, hi-power density constructions are commonplace to further minimize weight and bulk. And as a consequence of the high-power densities, more elaborate cooling schemes are required in such machines.
Most commonly, dynamoelectric machines utilized in aerospace environments are cooled through the use of hydraulic oil coolant that is pumped through cooling passages in both the rotor and the stator and other heat sensitive machine components. Of course, to reject heat from the hydraulic oil coolant, a hydraulic coolant oil to air heat exchanger is required. This in turn adds elements, expense, weight and bulk to the total dynamoelectric machine system. It also adds complexity in that coolant fittings must be such as to contain the hydraulic oil coolant at relatively high pressures and to prevent potentially hazardous leaks. Moreover, to provide coolant to rotating parts of the machines requires the presence of couplings which also adds to complexity and cost.
The problem is accentuated because many dynamoelectric machines operating in an aerospace environment operate at very high speeds to achieve the high power densities mentioned earlier and that, of course, requires greater precision and complexity of components.
Desirably, such a machine would be totally air-cooled. If that object could be obtained, system complexities associated with the hydraulic cooling circuit, and the associated weight and bulk are done away with entirely. The present invention is directed to achieving that object.